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Date: Wed, 03 Jan 2001 15:20:04
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Re: Re. VE1ZZ
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Mike is 200% right, just look at the meaning of ERP :
Effective Radiated Power

regarding Mals question : Why do the 'commercials' on LF use giant antennas ? 

1. Because they want a certain ERP (let's say 100kW) and in that range of
ERP it is cheaper to have a big antenna (at 50% efficiency) fed with 200kW
than a small antenna (at 1% efficiency) fed with 10MW.

2. Very high power into a small antenna will create additional problems (as
extreme voltage) that can be avoided with big antennas

But we hams live in a different world with our 1 Watt ERP restriction,
apart from legal limitations (building restrictions) a 30 or 40m tower will
be more expensive than a 2kW PA. So it often will be cheaper and easier to
get 1 Watt ERP with a smaller antenna and more power.

73, Rik  ON7YD

At 12:35 3/01/01 -0000, G3XDV wrote:
>G3KEV wrote:
>>So you are saying that 1W
>>erp from a dummy load radiates just as efficiently as 1W from a  200
>>ft vertical for instance. 
>
>and DK8KW retorted:
>> ... no, surely not! 
>
>But of course the statement is true. 1W ERP from a dummy load 
>inside a Faraday screeen inside lead-lined container will also 
>radiate as well as 1W ERP from a full sized dipole. The key word is 
>Radiated (the R in ERP). You will need an awful lot of megawatts 
>(gigawatts?) to get 1W ERP from such a dummy load but once that 
>watt is radiated there is no difference.
>
>
>
>Mike, G3XDV (IO91VT)
>http://www.lf.thersgb.net
>
>
>